Fix getTrainSpeed returning 0 for negative speeds (#2732) (#4415)

Refactor train speed handling to use GetTrainSpeed and SetTrainSpeed methods

Author: MohabCodeX

Server/mods/deathmatch/logic/CStaticFunctionDefinitions.cpp

@@ -5442,8 +5442,7 @@ bool CStaticFunctionDefinitions::GetTrainSpeed(CVehicle* pVehicle, float& fSpeed
     if (pVehicle->GetVehicleType() != VEHICLE_TRAIN)
         return false;
 
-    const CVector& vecVelocity = pVehicle->GetVelocity();
-    fSpeed = vecVelocity.Length();
+    fSpeed = pVehicle->GetTrainSpeed();
     return true;
 }
 
@@ -7330,6 +7329,7 @@ bool CStaticFunctionDefinitions::SetTrainSpeed(CVehicle* pVehicle, float fSpeed)
     vecVelocity.Normalize();
     vecVelocity *= fSpeed;
     pVehicle->SetVelocity(vecVelocity);
+    pVehicle->SetTrainSpeed(fSpeed);
 
     CBitStream BitStream;
     BitStream.pBitStream->Write(fSpeed);